DESCRIPTION: Leukocytes and platelets circulate throughout the blood freely, interacting with vessel walls only during inflammatory or thrombotic events. Integrins of the b3 family mediate many of the leukocyte and platelet adhesive events which are important in the resolution of inflammation and the prevention of blood loss. This proposal addresses the question of how b3 integrins are maintained in a non-adhesive state in the circulation and how they become activated to mediate adhesive events during disease states. The experiments detailed within test the hypothesis that the combined events of b3 integrin tyrosine phosphorylation and PKC activation are both required for leukocyte and platelet b3 integrin activation. b3-deficient leukocytes from genetically altered mice will be reconstituted with normal or tyrosine mutant b3 integrins and their functional capabilities assessed. Similarly, cell-permeant peptides will be used to disrupt the integrin-cytoskeleton interaction on the cytoplasmic face in human macrophages, platelets, and neutrophils. Phosphorylation of b3 induced by receptor ligation, likely permits the association of signaling molecules responsive to PKC. Experiments contained in this application will determine if the candidate molecule RACK1 binds to tyrosine phosphorylated b3 integrins and coordinates their response to PKC activation. Completion of these studies will enhance our knowledge of b3 integrin function in hematopoietic cells and provide new targets for therapeutic manipulation. Control of this receptor is important clinically in the prevention of unwarranted inflammation and thrombosis which can occur in natural pathologies and as the result of clinical therapies such as transplantation and vascular surgery.